Coccus

A coccus (plural cocci) is any bacterium that has a spherical, ovoid, or generally round shape.^[1] It is one of the three distinct bacterial shapes, the other two being bacillus (rod-shaped) and spiral-shaped cells.

Coccus is an English loanword of a modern or neo-Latin noun, which in turn stems from the Greek masculine noun kokkos (κόκκος) meaning "berry".^[2]

Arrangements

Cocci may occur as single cells or remain attached following cell division. Those that remain attached can be classified based on cellular arrangement:^[1]

Diplococci are pairs of cocci (e.g. Streptococcus pneumoniae and Neisseria gonorrhoeae)
Streptococci are chains of cocci (e.g. Streptococcus pyogenes).
Staphylococci are irregular (grape-like) clusters of cocci (e.g. Staphylococcus aureus).
Tetrads are clusters of four cocci arranged within the same plane (e.g. Micrococcus sp.).
Sarcina is a genus of bacteria that are found in cuboidal arrangements of eight cocci.

References

^ ^a ^b Pommerville, J.C. (2013). Fundamentals of Microbiology (10th ed.). Sudbury, MA: Jones & Bartlett. p. 106. ISBN 9781449647964.
^ κόκκος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project

[arrangement-1] Pommerville, J.C. (2013). Fundamentals of Microbiology (10th ed.). Sudbury, MA: Jones & Bartlett. p. 106. ISBN 9781449647964.

[2] κόκκος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project

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